[TheForge] Shop Air using Copper

[bistline at md.metrocast.net]

Trying to get hard air lines set up in my shop. Went to lowes to buy
"iron" pipe and noticed its made in Korea brand name Tuna. At many levels
that just bothers me. I turn around to see copper made in the USA. Believe
it or not the type L 3/4 copper is $1.25 a 10ft stick cheaper than the
"iron". I notice type m copper that is $5 cheaper yet. The type L has a
slightly thicker wall thickness. I know that the standard for air lines is
"iron pipe" however a little web searching has revealed copper is commonly
used.  Any inputs on copper for air lines?